How do I know?

I switched transmission in my van. I got the new
tranny from  an exact replica, (van, motor, tranny,
etc.) I have read so many horror stories about the
correct balance on a tranny, so what would I be
listening for or feeling if the  balance wasn't right. I
used the flex plate that was with the new
transmission although neither fp's had any weights
on them. I  just want to make sure that I have
everything right, I don't want mess this one up it
was so hard to find.